Controlled Radical Homopolymerization of Representative Cationically Polymerizable Vinyl Ethers

Abstract

Facile direct radical homopolymerization of vinyl ethers without a hydroxy group was achieved up to near full conversion. This polymerization was conducted in water suspension in the presence of lithium hydroxide using a thermally triggered azoinitiator of dimethyl 2,2′-azobis(2-methylpropionate). In the polymerization system, appropriate hydrogen bonding and cation−π interactions under basic conditions are keys to the successful direct radical homopolymerization. The hydrogen bonding between water and vinyl ether oxygen reduces the reactivity of the growing radical, thus suppressing unfavorable side reactions such as β-scission. In addition, Li + interacts with the oxygen and the vinyl group of vinyl ethers. The vinyl ether tends to be "activated" and the polymerization can be facilitated. Based on the results of free radical polymerization of vinyl ethers, controlled polymerization was also accomplished using the appropriate dithiocarbamate RAFT agent in view of the solubilities of the radical leaving group.

Recent Advances in Living Cationic Polymerization with Emerging Initiation/Controlling Systems

“…Although the Sugihara group has demonstrated that VEs can be transformed via a CRP mechanism, shielding new lights on the polymerization of electron‐rich monomers, quantitative lithium salts are required to tune the electronic property of monomers and promote the radical addition. [ 63 ]…”

Synthesis and cationic polymerization of halogen bonding vinyl ether monomers

“…1,2 With each passing year, an even wider scope of monomers are employed for all polymerization methods, and even previously held conceptions about what monomers are polymerizable or not using various methods are being contested. 3 As the toolbox to create polymers becomes more extensive, this enables a wide array of designed and functional self-assembly structures to be readily formed. While intermolecular interactions, such as hydrogen bonding or coordination bonds, can be reliably used to make many intriguing and useful supramolecular materials, these are not the only strong intermolecular interactions available.…”

Radical homopolymerization of vinyl ethers activated by Li+-π complexation in the presence of CH3OLi and LiI

“…Despite relatively mild reaction conditions, the addition of a radical to vinyl ethers usually produces a highly reactive σ-radical, which typically undergoes side reactions such as β-scission, frequent hydrogen abstraction and irreversible termination by propagating chain radicals. [1][2][3] Therefore, the direct radical polymerization of vinyl ethers has remained a tough challenge until Sugihara et al [4][5][6] recently reported the homopolymerization of vinyl ethers via complexation with LiOH in aqueous or hydrogen bonding in the bulk process. Indeed, alkyl vinyl ethers, especially with hydroxyl groups or halogen atoms, have been widely used as comonomers in special rubber, plastics, textiles, coatings, adhesives, additives, etc.…”

“…It is not strange that, aside from the studies on cationic living polymerization of vinyl ethers, there have been a few attempts to realize radical polymerization of non-radically polymerizable vinyl monomers through stabilizing the radical species. [4][5][6][34][35][36] Sugihara et al 4,5 first realized the radical homopolymerization of hydroxyl-functional vinyl ethers with the aid of hydrogen bonds between the oxygen atom and hydroxyl of the vinyl ether monomer, which effectively reduces the reactivity of growing chain radicals and inhibits side reactions such as β-scission. Then, they performed aqueous phase radical suspension polymerization of alkyl vinyl ethers with LiOH as a complexing agent (Li + ).…”